STUDIES IN PLANT POPULATION BIOLOGY: GRAYIA BRANDEGEI AND QUERCUS GAMBELII (HETERODICHOGAMY, UTAH, DIOECY, GENDER).

摘要

The reproductive biology of Grayia brandegei was examined. Although monoecious, Grayia brandegei exhibits a phenotypic dimorphism of protogynous and protandrous mating types known as heterodichogamy. Dichogamy, or the temporal separation of male and female flowering phases, appears to be complete. Flowering phases of protogynous and protandrous mating types are synchronized and reciprocal, ensuring cross-fertilization between mating types. No self-fertilization is possible in protandrous plants, but may be possible in protogynous plants if pistillate flowers remain unfertilized. Very little overlap of sexual functions occurred between plants of the same mating type. Within-type matings are likely rare. Mating type frequencies did not differ significantly from 1:1.;In a second study, three populations of Gambel oak (Quercus gambelii) were sampled for morphologic and enzymatic variation. A total of 11 leaf characters and 12 enzyme systems were examined. Two main trends in leaf morphology were noted using principal components analysis. The first trend corresponds to a measure of leaf size, the second to the degree of leaf lobing. Most of the morphologic variation was present at the population and clone levels. Little variation occurred either between or within boles. Of five interpretable enzyme systems, only the leucine amino peptidase (LAP) system was polymorphic. Based on correlations with life history parameters, we had anticipated a high degree of enzymatic variation.;Second specialization between mating types was also examined. Floral sex ratios of the two mating types differed significantly indicating some sexual specialization occurs. Sex ratios ranged from 0-38% female in protandrous and from 14-100% female in protogynous plants. Functional gender was determined for protogynous and protandrous plants of one subpopulation using the total number of viable seeds per plant. The result of 3.5% female for protandrous plants and 96.5% female for protogynous plants indicates a condition functionally close to dioecy. The gender specialization observed is likely due to ecological considerations.